U.S. patent number 6,798,958 [Application Number 10/245,299] was granted by the patent office on 2004-09-28 for cable with a high density of optical fibers.
This patent grant is currently assigned to Alcatel. Invention is credited to Vincent Bourget, Jean-Marc Kaczmarek.
United States Patent |
6,798,958 |
Bourget , et al. |
September 28, 2004 |
Cable with a high density of optical fibers
Abstract
A cable includes a tubular jacket which surrounds a plurality of
protection tubes in which optical fibers are accommodated in groups
and have a relative freedom of movement. These tubes are disposed
in layers in which they are disposed in a helix. The cable includes
at least one layer made up of an assembly of tubes which have an
outside diameter smaller than that of the tubes of a layer that
they surround and the tubes of the two layers all contain the same
number of optical fibers.
Inventors: |
Bourget; Vincent (Marly le Roi,
FR), Kaczmarek; Jean-Marc (Calais, FR) |
Assignee: |
Alcatel (Paris,
FR)
|
Family
ID: |
8867466 |
Appl.
No.: |
10/245,299 |
Filed: |
September 18, 2002 |
Foreign Application Priority Data
|
|
|
|
|
Sep 20, 2001 [FR] |
|
|
01 12158 |
|
Current U.S.
Class: |
385/113; 385/109;
385/111 |
Current CPC
Class: |
G02B
6/4413 (20130101) |
Current International
Class: |
G02B
6/44 (20060101); G02B 006/44 () |
Field of
Search: |
;385/109,111,113 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Patent Abstracts of Japan, vol. 1998, No. 11, Sep. 30, 1998 &
JP 10 170784 A (Hitachi Cable Ltd.), Jun. 26, 1998..
|
Primary Examiner: Lee; John D.
Assistant Examiner: Lin; Tina M
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
There is claimed:
1. An optical fiber cable including a tubular jacket which
surrounds a plurality of protection tubes disposed in layers and in
a helix within each layer, wherein said optical fibers are
accommodated in groups in which they have relative freedom of
movement, which cable includes at least one layer made up of an
assembly of tubes which have an outside diameter smaller than that
of said tubes of a layer that they surround and said tubes of said
two layers all contain the same number of optical fibers.
2. The optical fiber cable claimed in claim 1 wherein said cable
includes at least one layer made up of an assembly of tubes having
an outside diameter smaller than that of said tubes of the layer
that they surround, the ratios between the inside diameter and the
winding pitch of said tubes for these layers being chosen to obtain
an equivalent freedom of movement for said fibers regardless of the
layer.
3. The optical fiber cable claimed in claim 2 wherein the same
ratio between the inside diameter and the outside diameter of said
protector tubes is chosen for said tubes of the various layers.
4. The optical fiber cable claimed in claim 1, which includes
fibers which are distributed between said layers according to their
sensitivity, the tubes containing the more sensitive fibers forming
one or more layers surrounded by at least one layer in which the
tubes contain less sensitive fibers.
5. The optical fiber cable claimed in claim 1, wherein said tubes
containing said fibers are assembled in a regular manner to form
contiguous layers between the sheathing and a central bearing
member around which said layers are placed, the layer adjoining
said bearing member is made up of tubes having the same outside
diameter at least equal to that of said tubes of the other layers,
the layer adjoining the inside wall of the tube that forms said
sheathing is made up of tubes having the same outside diameter
smaller than that of the tubes of at least said layer adjoining
said bearing member, and the respective numbers of tubes in the
various layers are chosen to increase from said layer adjoining
said bearing member to said layer adjoining said inside wall of
said tube that forms said sheathing so that each layer is
continuous or virtually continuous.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on French Patent Application No. 01 12
158 filed Sep. 20, 2001, the disclosure of which is hereby
incorporated by reference thereto in its entirety, and the priority
of which is hereby claimed under 35 U.S.C. .sctn.119.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optical fiber cable with a high density
of fibers, of the type which includes a tubular jacket surrounding
a plurality of protection tubes in which groups of optical fibers
are housed. It relates more particularly to a cable comprising a
large number of fibers, in which the fiber protection tubes are
disposed in layers and helically within each layer.
2. Description of the Prior Art
Optical fiber cables of the type referred to above conventionally
include protection tubes for groups of optical fibers, the tubes
having a cross section slightly larger than would be sufficient to
accommodate the fibers of a group so that the fibers have some
freedom of movement within the tubes in the event of deformation of
the cable. This is known in the art. Combined with winding the
tubes in a helix, this limits the longitudinal forces, and in
particular the traction or compression forces, to which the optical
fibers of a cable are subjected when the cable is spooled, unwound
from a spool and/or bent, for example when spooling it for storage
or when installing it. These operations must be carried out without
exceeding predetermined mechanical limits for a cable with given
specifications, because of the fragile nature of the fibers. This
is also known in the art.
Thus research into optical fiber cables is currently being
undertaken with a view to obtaining the greatest possible density
of fibers in each cable to meet present and future demand for
optical transmission of information using fibers as the physical
transmission medium, whilst conforming to the mechanical
constraints imposed by use of such fibers in the cable, especially
during installation. The cables are ordinarily installed in
conduits, underground or in a technical tunnel. One field of
research aims to increase the number of fibers for the same outside
diameter of the cable and/or to reduce the diameter of a cable
accommodating a given number of fibers.
SUMMARY OF THE INVENTION
The invention therefore proposes an optical fiber cable including a
tubular jacket which surrounds a plurality of protection tubes
disposed in layers and in a helix within each layer, wherein the
optical fibers are accommodated and have a relative freedom of
movement.
According to one feature of the invention the cable includes at
least one layer made up of an assembly of tubes which have an
outside diameter smaller than that of the tubes of a layer that
they surround, although the tubes of the two layers each contain
the same number of optical fibers, to increase the capacity of the
cable and/or to limit its outside diameter relative to a cable
having layers in which the tubes have the same outside
diameter.
According to the invention the cable includes at least one layer
made up of an assembly of tubes having an outside diameter smaller
than that of the tubes of the layer that they surround, the ratios
between the inside diameter and the helical winding pitch for these
layers being chosen to obtain an equivalent freedom of movement for
the fibers regardless of the layer.
According to the invention the same ratio between the inside
diameter and the outside diameter of the protector tubes is chosen
for the tubes of the various layers.
In one embodiment of the invention, for use when the cable includes
fibers having different sensitivities to any significant
deformation, said fibers are distributed between the layers
according to their sensitivity, the tubes containing the more
sensitive fibers forming one or more layers surrounded by at least
one layer in which the tubes contain less sensitive fibers.
In a different embodiment of the invention the tubes containing the
fibers are assembled in a regular manner to form contiguous layers
between the sheathing and a central bearing member around which the
layers are placed. The layer adjoining the bearing member is made
up of tubes having the same outside diameter at least equal to that
of the tubes of the other layers, the layer adjoining the inside
wall of the tube that forms the sheathing is made up of tubes
having the same outside diameter smaller than that of the tubes of
at least the layer adjoining the bearing member, and the respective
numbers of tubes in the various layers are chosen to increase from
the layer adjoining the bearing member to the layer adjoining the
inside wall of the tube that forms the sheathing so that each layer
is virtually continuous.
The invention, its features and its advantages are explained in the
following description with reference to the figures mentioned
below.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a view in cross section of a prior art optical fiber
cable.
FIG. 2 shows a detail of one partly stripped end of a prior art
optical fiber cable.
FIG. 3 is a view in cross section of an optical fiber cable
according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The prior art optical fiber cable, a cross section of which is
shown in FIG. 1, includes a one-piece or composite tubular jacket
surrounding a plurality of protection tubes 1' housing groups of
the same number of optical fibers 2', for example twelve fibers per
group. The fibers 2' in a group have relative freedom of movement
within the tube 1' in which they extend side-by-side, for the
reason mentioned above. The function of the tubes 1' is to protect
the fibers from radial and longitudinal forces to which the optical
fiber cable may be subjected, and they are conventionally disposed
in concentric layers and in a helix with a constant or alternating
winding pitch, there being two such layers in the example shown.
The tubes usually have the same diameter if they all contain the
same number of fibers; their outside diameter is 2.5 mm, for
example, in the case of tubes receiving twelve glass optical
fibers. The same helical winding pitch P is conventionally adopted
for the protection tubes of one layer, as shown in FIG. 2 for a
theoretical cable example comprising a layer of tubes including two
representative tubes 1" and 1'". The tubes are wound with a helical
winding pitch P around a central bearing member 3" of the cable and
inside a protective tubular jacket 7".
The cable shown in FIG. 1 includes mechanical strength members to
prevent the application of excessive forces to the fibers, in
particular traction or bending forces when installing the cable.
This is known in the art.
In the example shown in FIG. 1, the cable includes a bearing member
4' which is more particularly intended to withstand longitudinal
forces applied to the cable. A strength structure 6' is included in
the jacket, in which it is situated between a sealing tape wrapping
5', inside which are housed the bearing member 4' and the
protection tubes 1' provided for the optical fibers 2', and an
external protection sheath 7'.
The above kind of cable jacket--combining a central bearing member
4 and an assembly including a strength structure 6, a sealing tape
wrapping 5 and an external protection sheath 7--is also shown in
FIG. 3, which relates to a cable according to the invention. This
architecture is shown by way of example only and must not be
considered as limiting on the invention.
The tubular cable jacket shown in FIG. 3 and comprising the
components 5, 6 and 7 can be manufactured in various ways and take
various forms. The bearing member 4 can be made from a resin
reinforced with glass fibers, from metal, or from any other
appropriate material. The strength structure 6 can take the force
of carbon fiber wicks, for example. The sealing tape wrapping 5
surrounds the tubes in which are housed the optical fibers 2 of the
cable and separates these tubes from the strength structure 6. The
external protection sheath 7 is made from a material that can be
extruded, for example, such as a fluorinated resin, a polyolefin, a
compound, etc.
According to the invention, there are two or more layers of tubes
around the bearing member 4 and inside the sealing tape wrapping 5,
as shown diagrammatically by way of example in FIG. 3.
The tubes in the layers preferably all house the same number of
optical fibers 2. According to the invention, at least one layer is
made up of an assembly of tubes which all have an outside diameter
smaller than that of the tubes of the layer that they surround,
such as the tubes of the layer including the tube 1A relative to
the tubes of the layer including the tube 1B.
In the embodiment shown, the tubes of the inner layer including the
tube 1B have an outside diameter of 2.5 mm, for example, whereas
the tubes of the outer layer including the tube 1A have an outside
diameter of 2 mm. If, as shown, the six tubes of the inner layer of
the cable shown in FIG. 1 and the six tubes of the inner layer of
the cable shown in FIG. 3 have the same outside diameter and
contain the same number of fibers, it is possible to dispose a
greater number of tubes on the outside layer of the cable shown in
FIG. 3 than on that of the cable shown in FIG. 1. This increase
corresponds to adding two tubes each containing twelve fibers to
the outer layer of the example shown, which implies reducing the
inside diameter of the tubes of the outer layer relative to that of
the inner layer. The diameter of the external envelope of the outer
layer, which in practical terms corresponds to the inside face of
the sealing tape wrapping 5, can therefore be reduced in the manner
shown in FIG. 3. Here this reduction is associated with an increase
in the density of the optical fiber cable and thus of its
transmission capacity. It can also be exploited to reduce the
outside diameter of the cable, or to be more precise of its
external protection sheath 7, compared to that of a prior art cable
of the kind shown in FIG. 1. Retaining the same cable outside
diameter and including a greater number of tubes and thus of
optical fibers in the various layers can of course be
envisaged.
In one particular embodiment of the invention the tubes in the
various layers, such as the tubes 1A and 1B, are manufactured with
the same ratio between their inside diameter and their outside
diameter (it must be borne in mind that the tubes in a layer have
the same outside diameter and therefore the same inside diameter).
The fact that the tubes of one layer, enveloped within another
layer, can have a larger inside diameter than the tubes of said
other layer is therefore reflected in a reduction in the freedom of
movement of the fibers contained in the tubes of the surrounding
layer relative to that obtained for the fibers contained in the
tubes of the surrounded layer, if the fibers have the same outside
diameter in all the tubes. To compensate this reduction in the
freedom of movement of the fibers contained in the tubes of a
surrounding layer relative to that obtained for the fibers
contained in the smaller inside diameter tubes of an surrounded
layer, a helical winding pitch P is therefore used for the tubes of
the surrounding layer that is at least the same as, and preferably
greater than, for those of the surrounded layer. The respective
winding pitches are determined in a manner that is known to the
person skilled in the art as a function of the characteristics of
the layers of tubes so that an equivalent freedom of movement is
obtained for the optical fibers in the various layers of tubes in
the cable.
In another particular embodiment of the invention, cables can be
produced which include optical fibers which have different
sensitivities to any deformation to which they may be subjected, in
particular when unwinding the cable from a spool and installing it.
Such deformation can in particular be caused by unwinding the cable
from a spool and installing it, especially when installing it
involves inserting it into a conduit or into a technical tunnel
that exists already or covering the cable. The deformation that
occurs under the above conditions is known, as a general rule, to
be more difficult to control than those to which the cable is
subjected during spooling, at the end of the manufacturing
process.
The invention therefore distributes the fibers between the layers
as a function of their respective sensitivity, the more sensitive
fibers being housed in the tubes of at least one layer which is
surrounded by at least one other layer of tubes containing less
sensitive fibers and thus better able to withstand forces
transmitted to the cable, in particular when the cable is bent in a
localized manner.
The cable shown in FIG. 3 includes protection tubes, such as the
tubes 1A and 1B, which are assembled in a regular manner to form
contiguous layers between the sheathing and a bearing member 4. Two
layers are shown here, it being understood that this number can be
increased, as already indicated. The layer adjoining the bearing
member 4 is made up of tubes, such as the tube 1B, having the same
outside diameter, for example 2.5 mm, which is at least equal to
that of the tubes of the other layer or layers. The layer adjoining
the inside wall of the sheathing tube, thus in this example the
inside face of the sealing tape wrapping 5, is made up of tubes
having the same external diameter, for example 2 mm, which is
smaller than that of the tubes of at least the layer adjoining the
bearing member 4. The number of tubes for each layer is chosen so
that the layer is continuous or virtually continuous. The inside
diameters of the tubes and the pitch for simple or alternating
helical winding of the tubes in layers are such that the optical
fibers have practically the same freedom of movement regardless of
the layer in which they are situated.
* * * * *